Unconfined liquid-phase microextraction

Abstract Unconfined liquid-phase microextraction (LPME) involves those techniques where the extractant phase is not separated from the donor by a physical barrier. The use of extractant in the low microliter range was first proposed in the middle 1990s, and since then, the field has evolved rapidly. In this evolution, several and well-defined research lines can be highlighted, namely: (1) the application of new solvents with better performance (e.g., higher enrichment capacity, safer to operators and the environment), (2) the development of new techniques and the improvement of the existing ones, and (3) the automation of an even integration of the LPME with instrumental techniques. Since the first topic will be considered in depth in another section of the book, this chapter is focused on the latter lines. The description of classical liquid–liquid extraction is the starting point of the chapter as it provides a general overview of the fundamentals (applicable to LPME) and the limitations of the original technique. These limitations are the driving force for the development of the microextraction approaches. The chapter will describe two main groups of techniques. Initially, those based on a single drop (with diverse volumes) will be presented. The second part of the chapter will be focused on those techniques that try to increase the acceptor–donor phases contact area for better performance (rapidity and efficiency). This chapter will be complemented with the subsequent one, where the main confined LPME techniques are discussed.